A steering angle of a steering column of a vehicle can be used for controlling steering systems, suspension systems, and braking systems. Typically, steering, sensors are used for measuring the steering angle. The steering sensors are installed and calibrated at the time the vehicle is manufactured. However, the re-calibration of the steering sensors is needed whenever the steering system geometry is changed due to the operation of the vehicle.
Some conventional methods determine steering angle by detecting straight motion of the vehicle and adjusting the steering offset of the steering sensor during that straight motion. See, e.g., U.S. 2010/235,052 U.S. Pat. No. 5,465,210 or U.S. 2009/0125187. However, it is not always possible to accurately detect the straight movement of the vehicle due to the curvature of the surface of the road. Also, there may be relatively few periods when the vehicle is actually di mg perfectly straight and hence significant time may pass before the determination occurs. Accordingly, there is a need for accurate determination of the steering angle without relying on the straight motion of the vehicle.
Some methods calibrate the steering sensor based on detailed models of the vehicle dynamics. See, e.g., U.S. Pat. No. 6,775,604 or U.S. Pat. No. 6,498,971. However, these models require knowledge of the road friction and various vehicle parameters, such as mass, inertia, tire stiffness, weight distribution, and suspension angles. Such knowledge is difficult and almost impossible to obtain during an operation of the vehicle. Also, the models change over the time due to wear of the tires and changes in the vehicle mass.
Accordingly, there is a need in the art to determine the steering angle during the operation of the vehicle, it is also desired to determine the steering angle when the vehicle experiences the lateral motion. It is also desired to determine the steering angle without the use of detailed vehicle models.